The full form of Rj12 connector is registered jack 12. It is a connection jack that enjoins a central telephone system with single telephone lines through a line circuit. The Rj12 uses a 6P6C connector. It has six slots for connection wearing and all six slots are used for communication.
1. RJ12 is the most common, being used on flat line cords that connect the base of a telephone to the wall. RJ11 is an older version of RJ12, and they are the same size. The difference is that RJ11 uses four internal wires (called conductors) while RJ12 uses six.
2. The key difference between the two is the size of the plastic connectors on the ends of the cable. Telephones use an RJ11/RJ12 connector whereas Ethernet uses RJ45. RJ11/RJ12 only uses 4-6 pins whereas RJ45 uses 8 pins.